The present invention relates to a deep recording/reproducing apparatus and video signal recording format and method therefor, in which a video signal is recorded on a deep level of a recording medium in units of screens in addition to a signal recorded on the surface level thereof, and in which the deeply recorded signal is reproducible during multifunctional operations.
In a general analog video cassette recorder (hereinafter referred to as a VCR), in recording one screen (one frame) of a video signal on a recording medium such as tape, a dual-channel video track is used. A first field (the odd field) of the video signal is recorded on one channel of the video track, and a second field (the even field) thereof is recorded on the other channel.
In such a VCR, a multifunctional operation (i.e., fast forward, rewind, high-speed search, etc.) creates noise due to the fact that a head reproduces while crossing tracks. Because of this problem, a double-azimuth four head configuration has been employed in such analog VCRs so that a picture without noise is obtained even during such multifunctional operation.
Meanwhile, to satisfy the increasing demand for recording and reproducing a high-quality picture, a digital VCR (D-VCR) has been presented along with high-definition television.
In such D-VCRs, to precisely record and reproduce video information, velocity control is required. For this, a drum servo and capstan servo are provided as in FIG. 1. The function of the drum servo is such that when a video head attached to a drum tracks tape, the video head is rotated at a predetermined velocity and phase. The capstan servo functions so as to move the tape at a predetermined velocity and phase. As illustrated in FIG. 2A, the relative velocity of the drum is vector-synthesized with the drum velocity and capstan velocity.
During normal-speed playback, as shown in FIG. 2B, tracks are traced along the same head track as used during recording.
In a VHS VCR, high-speed playback is performed in addition to normal-speed playback. In this case due to the increase of capstan motor speed, the tracks cannot be traced along the same head track as used during recording, as shown in FIG. 2C. However, in an analog VCR having double-azimuth four heads, since the correlation between fields is high as shown in FIG. 3A, even during high-speed playback, image synthesis is facilitated and a high-speed-reproduced picture is obtained without difficulty as shown in FIG. 3B.
However, a digital VCR experiences problems during high-speed playback due to the following reasons.
First, in digital VCRs, when analog information is converted into digital form, the amount of information is increased so that one frame of information is stored onto four fields (tracks), and the correlation between fields is very low. This is because the video source is shuffled so as to eliminate burst errors due to inherent tape defects. When the shuffling is performed, the burst errors become random errors which have an error dispersion effect greater than the burst errors, to improve picture quality. In this shuffling, however, the correlation between fields is greatly lowered to thereby hinder image reconstruction.
Secondly, since the digitized signal is recorded by data compression, when data expansion is performed during high-speed playback, the high-speed playback should be carried out in sync units so as to restore the data. Here, image reconstruction is achieved according to location information. If the high-speed playback is not performed in sync units, data expansion is impossible due to the incomplete reading of data.
Meanwhile, the digital VCR uses four video tracks (segments) when one frame of video signals is recorded on tape. A digital signal is error-corrected according to an error correction code (ECC). However, if an error which cannot be error-corrected by the ECC is created, since the error adversely affects picture quality, one frame of the digital video signal is divided into segments and recorded on four video tracks, thereby preventing error-generated noise.
A video signal recording/reproducing apparatus having a variable playback velocity in which, during the recording of a video signal according to a segment method, each segment is recorded on different video tracks, is disclosed in U.S. Pat. No. 4,887,169.
In the above disclosure, a segment index signal is inserted and recorded during the horizontal blanking period of each segment. The index signal is detected from a reproduced signal only during high-speed playback, not during normal-speed playback so that sequentially reproduced signals according to the index signal are temporarily stored in a memory and are output according to the control signal of a controller. Since the apparatus requires the index signal for high-speed playback, however, increased overhead of data (parity data) occurs.
Further, a method has been proposed in which one screen of a digital video signal is additionally recorded on an expected traveling track of a head during multifunctional operation so as to enable a high-speed search. However, this method involves technical difficulties in that the traveling track must be precisely predicted. The method also exhibits a limited enhancement of picture quality and complicated hardware.
Furthermore, a VHS hi-fi method is well-known in which an audio FM signal is recorded on a deep level of the magnetic substance of a tape and a video signal is recorded on a surface level thereof. In this method, first, signals are recorded on the deep level using a strong magnetic field, and then signals are recorded on the surface portion using a weak magnetic field. Such a hi-fi VCR is disclosed in U.S. Pat. No. 4,757,394.